Radio Link Monitoring and Cell Search Techniques for High Movement Speeds

ABSTRACT

This disclosure relates to techniques for performing radio link monitoring and cell searching when moving at high speeds. A movement speed of a wireless device may be determined. When performing a cell search, the manner of the cell search may depend on the movement speed of the wireless device, potentially including cells that are associated with high movement speed being more highly prioritized when the wireless device is determined to be at a higher movement speed than when the wireless device is determined to be at a lower movement speed.

FIELD OF THE INVENTION

The present application relates to wireless communications, and moreparticularly to systems, apparatuses, and methods for performing radiolink monitoring and cell searching when moving at high speeds.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. In recentyears, wireless devices such as smart phones and tablet computers havebecome increasingly sophisticated. In addition to supporting telephonecalls, many mobile devices (e.g., user equipment devices or UEs) nowprovide access to the internet, email, text messaging, and navigationusing the global positioning system (GPS), and are capable of operatingsophisticated applications that utilize these functionalities.Additionally, there exist numerous different wireless communicationtechnologies and standards. Some examples of wireless communicationstandards include GSM, UMTS (associated with, for example, WCDMA orTD-SCDMA air interfaces), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN orWi-Fi), BLUETOOTH™, etc.

The ever increasing number of features and functionality introduced inwireless communication devices also creates a continuous need forimprovement in both wireless communications and in wirelesscommunication devices. In particular, it is important to ensure theaccuracy of transmitted and received signals through wireless devicesused in wireless cellular communications. In addition, increasing thefunctionality of a UE device can place a significant strain on thebattery life of the UE device. Thus it is very important to also reducepower requirements in UE device designs while allowing the UE device tomaintain good transmit and receive abilities for improvedcommunications.

Additionally, wireless devices are used in an increasing range ofcontexts. For example, wireless devices may be used at a variety ofmovement speeds, e.g., ranging from relatively stationary or slowmovement speeds (e.g., devices in fixed locations or carried bypedestrians) to very high speeds (e.g., high speed trains, etc.).Different techniques and features may provide better performance underdifferent such conditions, at least in some instances. Accordingly,improvements in the field are desired.

SUMMARY OF THE INVENTION

Embodiments are presented herein of apparatuses, systems, and methodsfor performing radio link monitoring and cell searching when moving athigh speeds.

Among the techniques described herein are included techniques fordetermining the movement speed of a wireless device, including by usingGPS capabilities, motion sensing capabilities, and/or the doppler shiftof cellular signals received by the wireless device. Additionally,techniques are described for determining the movement speed or evenwhether a wireless device is in a high speed train scenario (e.g., as apotential additional or alternative determination to the movement speedof the wireless device) based on the cell history of the wirelessdevice, for example based on how recently and/or how often the wirelessdevice has camped on a cell associated with high movement speed, such asa cell in a high speed train network.

It is further described herein that a wireless device may perform cellsearching based at least in part on the movement speed of the wirelessdevice, e.g., as may be determined using any of the techniques describedherein. For example, cells of a high speed train network may beprioritized during cell searches when a wireless device determines thatit has a high movement speed and/or is in a high speed train scenariorelative to times when the wireless device determines that it does nothave a high movement speed and/or is not in a high speed train scenario.

Still further, it is described herein that a wireless device may performradio link monitoring based at least in part on the movement speed ofthe wireless device. For example, one or more radio link parameters maybe modified to more quickly and/or aggressively declare radio linkfailure when a wireless device determines that it has a high movementspeed and/or is in a high speed train scenario relative to times whenthe wireless device determines that it does not have a high movementspeed and/or is not in a high speed train scenario.

Note that the techniques described herein may be implemented in and/orused with a number of different types of devices, including but notlimited to base stations, access points, cellular phones, portable mediaplayers, tablet computers, wearable devices, and various other computingdevices.

This Summary is intended to provide a brief overview of some of thesubject matter described in this document. Accordingly, it will beappreciated that the above-described features are merely examples andshould not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, andadvantages of the subject matter described herein will become apparentfrom the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to some embodiments;

FIG. 2 illustrates an exemplary base station in communication with anexemplary wireless user equipment (UE) device, according to someembodiments;

FIG. 3 illustrates an exemplary block diagram of a UE, according to someembodiments;

FIG. 4 illustrates an exemplary block diagram of a base station,according to some embodiments;

FIG. 5 is a flowchart diagram illustrating aspects of an exemplarypossible method for performing radio link monitoring and cell searchingbased at least in part on movement speed, according to some embodiments;

FIG. 6 is a graph illustrating a possible movement speed timeline for awireless device on a high speed train, according to some embodiments;

FIG. 7 is a flowchart diagram illustrating aspects of an exemplarypossible method for determining whether a wireless device is travellingat high speed, according to some embodiments;

FIG. 8 is a state diagram illustrating possible states and statetransitions that could be used for monitoring whether a wireless deviceis in a high movement speed state, according to some embodiments;

FIG. 9 is a diagram illustrating exemplary possible cell transitions fora wireless device moving on a high speed train, according to someembodiments;

FIG. 10 is a flowchart diagram illustrating aspects of an exemplarypossible method for performing a cell scan after a radio link failureevent when a wireless device is moving at a high movement speed,according to some embodiments; and

FIGS. 11-12 are flowchart diagrams illustrating aspects of exemplarypossible methods for performing radio link monitoring based at least inpart on movement speed, according to some embodiments.

While features described herein are susceptible to various modificationsand alternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to be limiting to the particular form disclosed, but onthe contrary, the intention is to cover all modifications, equivalentsand alternatives falling within the spirit and scope of the subjectmatter as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS Acronyms

Various acronyms are used throughout the present application.Definitions of the most prominently used acronyms that may appearthroughout the present application are provided below:

-   -   UE: User Equipment    -   RF: Radio Frequency    -   BS: Base Station    -   GSM: Global System for Mobile Communication    -   UMTS: Universal Mobile Telecommunication System    -   LTE: Long Term Evolution    -   NR: New Radio    -   TX: Transmission/Transmit    -   RX: Reception/Receive    -   LAN: Local Area Network    -   WLAN: Wireless LAN    -   AP: Access Point    -   RAT: Radio Access Technology    -   IEEE: Institute of Electrical and Electronics Engineers    -   Wi-Fi: Wireless Local Area Network (WLAN) RAT based on the IEEE        802.11 standards

Terms

The following is a glossary of terms that may appear in the presentapplication:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium maycomprise other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer system for execution. The term “memory medium” may include twoor more memory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Computer System (or Computer)—any of various types of computing orprocessing systems, including a personal computer system (PC), mainframecomputer system, workstation, network appliance, Internet appliance,personal digital assistant (PDA), television system, grid computingsystem, or other device or combinations of devices. In general, the term“computer system” may be broadly defined to encompass any device (orcombination of devices) having at least one processor that executesinstructions from a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), tablet computers(e.g., iPad™, Samsung Galaxy™), portable gaming devices (e.g., NintendoDS™, PlayStation Portable™, Gameboy Advance™, iPhone™), wearable devices(e.g., smart watch, smart glasses), laptops, PDAs, portable Internetdevices, music players, data storage devices, or other handheld devices,etc. In general, the term “UE” or “UE device” can be broadly defined toencompass any electronic, computing, and/or telecommunications device(or combination of devices) which is easily transported by a user andcapable of wireless communication.

Wireless Device—any of various types of computer system devices whichperforms wireless communications. A wireless device can be portable (ormobile) or may be stationary or fixed at a certain location. A UE is anexample of a wireless device.

Communication Device—any of various types of computer systems or devicesthat perform communications, where the communications can be wired orwireless. A communication device can be portable (or mobile) or may bestationary or fixed at a certain location. A wireless device is anexample of a communication device. A UE is another example of acommunication device.

Base Station (BS)—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements that are capable of performing a function in a device, e.g. ina user equipment device or in a cellular network device. Processingelements may include, for example: processors and associated memory,portions or circuits of individual processor cores, entire processorcores, processor arrays, circuits such as an ASIC (Application SpecificIntegrated Circuit), programmable hardware elements such as a fieldprogrammable gate array (FPGA), as well any of various combinations ofthe above.

Wi-Fi—The term “Wi-Fi” has the full breadth of its ordinary meaning, andat least includes a wireless communication network or RAT that isserviced by wireless LAN (WLAN) access points and which providesconnectivity through these access points to the Internet. Most modernWi-Fi networks (or WLAN networks) are based on IEEE 802.11 standards andare marketed under the name “Wi-Fi”. A Wi-Fi (WLAN) network is differentfrom a cellular network.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

Configured to—Various components may be described as “configured to”perform a task or tasks. In such contexts, “configured to” is a broadrecitation generally meaning “having structure that” performs the taskor tasks during operation. As such, the component can be configured toperform the task even when the component is not currently performingthat task (e.g., a set of electrical conductors may be configured toelectrically connect a module to another module, even when the twomodules are not connected). In some contexts, “configured to” may be abroad recitation of structure generally meaning “having circuitry that”performs the task or tasks during operation. As such, the component canbe configured to perform the task even when the component is notcurrently on. In general, the circuitry that forms the structurecorresponding to “configured to” may include hardware circuits.

Various components may be described as performing a task or tasks, forconvenience in the description. Such descriptions should be interpretedas including the phrase “configured to.” Reciting a component that isconfigured to perform one or more tasks is expressly intended not toinvoke 35 U.S.C. § 112, paragraph six, interpretation for thatcomponent.

FIGS. 1 and 2—Exemplary Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem in which aspects of this disclosure may be implemented, accordingto some embodiments. It is noted that the system of FIG. 1 is merely oneexample of a possible system, and embodiments may be implemented in anyof various systems, as desired.

As shown, the exemplary wireless communication system includes a basestation 102 which communicates over a transmission medium with one ormore (e.g., an arbitrary number of) user devices 106A, 106B, etc.through 106N. Each of the user devices may be referred to herein as a“user equipment” (UE) or UE device. Thus, the user devices 106 arereferred to as UEs or UE devices.

The base station 102 may be a base transceiver station (BTS) or cellsite, and may include hardware and/or software that enables wirelesscommunication with the UEs 106A through 106N. If the base station 102 isimplemented in the context of LTE, it may alternately be referred to asan ‘eNodeB’ or ‘eNB’. If the base station 102 is implemented in thecontext of 5G NR, it may alternately be referred to as a ‘gNodeB’ or‘gNB’. The base station 102 may also be equipped to communicate with anetwork 100 (e.g., a core network of a cellular service provider, atelecommunication network such as a public switched telephone network(PSTN), and/or the Internet, among various possibilities). Thus, thebase station 102 may facilitate communication among the user devicesand/or between the user devices and the network 100. The communicationarea (or coverage area) of the base station may be referred to as a“cell.” As also used herein, from the perspective of UEs, a base stationmay sometimes be considered as representing the network insofar asuplink and downlink communications of the UE are concerned. Thus, a UEcommunicating with one or more base stations in the network may also beinterpreted as the UE communicating with the network.

The base station 102 and the user devices may be configured tocommunicate over the transmission medium using any of various radioaccess technologies (RATs), also referred to as wireless communicationtechnologies, or telecommunication standards, such as GSM. UMTS (WCDMA),LTE, LTE-Advanced (LTE-A), LAA/LTE-U, 5G NR, 3GPP2 CDMA2000 (e.g.,1×RTT, 1×EV-DO, HRPD, eHRPD), Wi-Fi, WiMAX etc.

Base station 102 and other similar base stations operating according tothe same or a different cellular communication standard may thus beprovided as one or more networks of cells, which may provide continuousor nearly continuous overlapping service to UE 106 and similar devicesover a geographic area via one or more cellular communication standards.

Note that a UE 106 may be capable of communicating using multiplewireless communication standards. For example, a UE 106 might beconfigured to communicate using either or both of a 3GPP cellularcommunication standard or a 3GPP2 cellular communication standard. Insome embodiments, the UE 106 may be configured to perform cell searchesand/or radio link monitoring in a manner based at least in part on themovement speed of the UE 106, at least according to the various methodsas described herein. The UE 106 might also or alternatively beconfigured to communicate using WLAN, BLUETOOTH™, one or more globalnavigational satellite systems (GNSS, e.g., GPS or GLONASS), one and/ormore mobile television broadcasting standards (e.g., ATSC-M/H or DVB-H),etc. Other combinations of wireless communication standards (includingmore than two wireless communication standards) are also possible.

FIG. 2 illustrates an exemplary user equipment 106 (e.g., one of thedevices 106A through 106N) in communication with the base station 102,according to some embodiments. The UE 106 may be a device with wirelessnetwork connectivity such as a mobile phone, a handheld device, awearable device, a computer or a tablet, or virtually any type ofwireless device. The UE 106 may include a processor that is configuredto execute program instructions stored in memory. The UE 106 may performany of the method embodiments described herein by executing such storedinstructions. Alternatively, or in addition, the UE 106 may include aprogrammable hardware element such as an FPGA (field-programmable gatearray) that is configured to perform any of the method embodimentsdescribed herein, or any portion of any of the method embodimentsdescribed herein. The UE 106 may be configured to communicate using anyof multiple wireless communication protocols. For example, the UE 106may be configured to communicate using two or more of CDMA2000, LTE,LTE-A, 5G NR, WLAN, or GNSS. Other combinations of wirelesscommunication standards are also possible.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols according to one or more RATstandards. In some embodiments, the UE 106 may share one or more partsof a receive chain and/or transmit chain between multiple wirelesscommunication standards. The shared radio may include a single antenna,or may include multiple antennas (e.g., for MIMO) for performingwireless communications. In general, a radio may include any combinationof a baseband processor, analog RF signal processing circuitry (e.g.,including filters, mixers, oscillators, amplifiers, etc.), or digitalprocessing circuitry (e.g., for digital modulation as well as otherdigital processing). Similarly, the radio may implement one or morereceive and transmit chains using the aforementioned hardware.

In some embodiments, the UE 106 may include separate transmit and/orreceive chains (e.g., including separate antennas and other radiocomponents) for each wireless communication protocol with which it isconfigured to communicate. As a further possibility, the UE 106 mayinclude one or more radios that are shared between multiple wirelesscommunication protocols, and one or more radios that are usedexclusively by a single wireless communication protocol. For example,the UE 106 may include a shared radio for communicating using either ofLTE or CDMA2000 1×RTT (or LTE or GSM), and separate radios forcommunicating using each of Wi-Fi and BLUETOOTH™. Other configurationsare also possible.

FIG. 3—Block Diagram of an Exemplary UE Device

FIG. 3 illustrates a block diagram of an exemplary UE 106, according tosome embodiments. As shown, the UE 106 may include a system on chip(SOC) 300, which may include portions for various purposes. For example,as shown, the SOC 300 may include processor(s) 302 which may executeprogram instructions for the UE 106 and display circuitry 304 which mayperform graphics processing and provide display signals to the display360. The SOC 300 may also include motion sensing circuitry 370 which maydetect motion of the UE 106, for example using a gyroscope,accelerometer, and/or any of various other motion sensing components.The processor(s) 302 may also be coupled to memory management unit (MMU)340, which may be configured to receive addresses from the processor(s)302 and translate those addresses to locations in memory (e.g., memory306, read only memory (ROM) 350, NAND flash memory 310) and/or to othercircuits or devices, such as the display circuitry 304, radio 330,connector I/F 320, and/or display 360. The MMU 340 may be configured toperform memory protection and page table translation or set up. In someembodiments, the MMU 340 may be included as a portion of theprocessor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including NAND flash 310), a connector interface 320 (e.g., for couplingto the computer system), the display 360, and wireless communicationcircuitry 330 (e.g., for LTE, LTE-A, NR, CDMA2000, BLUETOOTH™, Wi-Fi,GPS, etc.). The UE device 106 may include at least one antenna (e.g. 335a), and possibly multiple antennas (e.g. illustrated by antennas 335 aand 335 b), for performing wireless communication with base stationsand/or other devices. Antennas 335 a and 335 b are shown by way ofexample, and UE device 106 may include fewer or more antennas. Overall,the one or more antennas are collectively referred to as antenna 335.For example, the UE device 106 may use antenna 335 to perform thewireless communication with the aid of radio circuitry 330. As notedabove, the UE may be configured to communicate wirelessly using multiplewireless communication standards in some embodiments.

As described further subsequently herein, the UE 106 (and/or basestation 102) may include hardware and software components forimplementing methods for at least UE 106 to perform cell searches and/orradio link monitoring in a manner based at least in part on the movementspeed of the UE 106. The processor(s) 302 of the UE device 106 may beconfigured to implement part or all of the methods described herein,e.g., by executing program instructions stored on a memory medium (e.g.,a non-transitory computer-readable memory medium). In other embodiments,processor(s) 302 may be configured as a programmable hardware element,such as an FPGA (Field Programmable Gate Array), or as an ASIC(Application Specific Integrated Circuit). Furthermore, processor(s) 302may be coupled to and/or may interoperate with other components as shownin FIG. 3, to perform cell searches and/or radio link monitoring in amanner based at least in part on movement speed according to variousembodiments disclosed herein. Processor(s) 302 may also implementvarious other applications and/or end-user applications running on UE106.

In some embodiments, radio 330 may include separate controllersdedicated to controlling communications for various respective RATstandards. For example, as shown in FIG. 3, radio 330 may include aWi-Fi controller 350, a cellular controller (e.g. NR controller) 352,and BLUETOOTH™ controller 354, and in at least some embodiments, one ormore or all of these controllers may be implemented as respectiveintegrated circuits (ICs or chips, for short) in communication with eachother and with SOC 300 (and more specifically with processor(s) 302).For example, Wi-Fi controller 350 may communicate with cellularcontroller 352 over a cell-ISM link or WCI interface, and/or BLUETOOTH™controller 354 may communicate with cellular controller 352 over acell-ISM link, etc. While three separate controllers are illustratedwithin radio 330, other embodiments have fewer or more similarcontrollers for various different RATs that may be implemented in UEdevice 106.

Further, embodiments in which controllers may implement functionalityassociated with multiple radio access technologies are also envisioned.For example, according to some embodiments, the cellular controller 352may, in addition to hardware and/or software components for performingcellular communication, include hardware and/or software components forperforming Wi-Fi preamble detection, e.g., for detecting Wi-Fi physicallayer preambles transmitted in unlicensed frequency bands that might berelevant to possible communication in unlicensed spectrum by the UE 106.As another possibility, the cellular controller 352 may include hardwareand/or software components for generating Wi-Fi physical layer preamblesignals, e.g., for transmitting as part of uplink communications by theUE 106 that occur in unlicensed frequency bands.

FIG. 4—Block Diagram of an Exemplary Base Station

FIG. 4 illustrates a block diagram of an exemplary base station 102,according to some embodiments. It is noted that the base station of FIG.4 is merely one example of a possible base station. As shown, the basestation 102 may include processor(s) 404 which may execute programinstructions for the base station 102. The processor(s) 404 may also becoupled to memory management unit (MMU) 440, which may be configured toreceive addresses from the processor(s) 404 and translate thoseaddresses to locations in memory (e.g., memory 460 and read only memory(ROM) 450) or to other circuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above in FIGS. 1 and 2. The network port470 (or an additional network port) may also or alternatively beconfigured to couple to a cellular network, e.g., a core network of acellular service provider. The core network may provide mobility relatedservices and/or other services to a plurality of devices, such as UEdevices 106. In some cases, the network port 470 may couple to atelephone network via the core network, and/or the core network mayprovide a telephone network (e.g., among other UE devices serviced bythe cellular service provider).

The base station 102 may include at least one antenna 434, and possiblymultiple antennas. The antenna(s) 434 may be configured to operate as awireless transceiver and may be further configured to communicate withUE devices 106 via radio 430. The antenna(s) 434 communicates with theradio 430 via communication chain 432. Communication chain 432 may be areceive chain, a transmit chain or both. The radio 430 may be designedto communicate via various wireless telecommunication standards,including, but not limited to, NR, LTE, LTE-A WCDMA, CDMA2000, etc. Theprocessor 404 of the base station 102 may be configured to implementand/or support implementation of part or all of the methods describedherein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium).Alternatively, the processor 404 may be configured as a programmablehardware element, such as an FPGA (Field Programmable Gate Array), or asan ASIC (Application Specific Integrated Circuit), or a combinationthereof. In the case of certain RATs, for example Wi-Fi, base station102 may be designed as an access point (AP), in which case network port470 may be implemented to provide access to a wide area network and/orlocal area network (s), e.g. it may include at least one Ethernet port,and radio 430 may be designed to communicate according to the Wi-Fistandard. The base station 102 may operate according to the variousmethods as disclosed herein for wireless devices to perform cellsearches and/or radio link monitoring in a manner based at least in parton wireless device movement speed.

FIG. 5—Movement Speed Based Cell Searching and Radio Link Monitoring

As wireless device usage grows generally, wireless devices are beingused in an increasingly wide range of contexts. One such increasinglywide usage range may include the movement speed of a wireless device.Users may at times utilize their wireless devices when stationary, atpedestrian movement speeds, in motor vehicles, and while in even higherspeed forms of transport such as high-speed trains, among variouspossibilities. The movement speed of a wireless device may have avariety of possible effects on the operation of the wireless device. Forexample, a wireless device moving at a high speed may move from one cellto another more frequently than a wireless device moving at a lowerspeed, and each such transition between cells may progress according toa more abbreviated timeline. Provided a wireless device can determine atwhat speed it is currently moving with sufficient accuracy, it mayaccordingly be possible to modify certain behaviors of the wirelessdevice in accordance with the movement speed of the wireless device, topotentially improve user experience, reduce power consumption, and/orotherwise provide improved operating characteristics.

Accordingly, FIG. 5 is a flowchart diagram illustrating a method for awireless device (e.g., a cellular base station or wireless userequipment (UE) device) to perform cell searches and/or radio linkmonitoring in a manner based at least in part on the movement speed ofthe wireless device, according to some embodiments.

Aspects of the method of FIG. 5 may be implemented by a wireless device(such as a UE 106 illustrated in and described with respect to variousof the Figures herein), or more generally in conjunction with any of thecomputer systems or devices shown in the above Figures, among otherdevices, as desired. Note that while at least some elements of themethod of FIG. 5 are described in a manner relating to the use ofcommunication techniques and/or features associated with LTE and/or 3GPPspecification documents, such description is not intended to be limitingto the disclosure, and aspects of the method of FIG. 5 may be used inany suitable wireless communication system, as desired. In variousembodiments, some of the elements of the methods shown may be performedconcurrently, in a different order than shown, may be substituted for byother method elements, or may be omitted. Additional method elements mayalso be performed as desired. As shown, the method of FIG. 5 may operateas follows.

In 502, the movement speed of the wireless device may be determined. Themovement speed determination may be performed in any of various manners,based on any of various possible conditions, as desired.

One possible consideration may include a speed or velocity calculationbased on information gathered from a global positioning system (GPS) orother global navigational satellite system (GNSS) module of the wirelessdevice. For example, the wireless device may be able to determine itsposition as it changes over time and estimate the current speed orvelocity of the wireless device based on the magnitude of the change indetected position over time.

Another possible consideration may include a velocity or speedcalculation based on measurements performed by motion detectioncircuitry of the wireless device. For example, the motion detectioncircuitry may be configured to detect acceleration and/or deceleration,which may thus be useful to determine changes to movement speed and/orto infer or estimate current movement speed or velocity.

A further possible consideration may include an amount of doppler shiftdetected in cellular communication signals received by the wirelessdevice. For example, if a wireless device is camped on a cell, thewireless device may be able to deduce its velocity based on theaccumulated doppler shift of received signals relative to the carrierfrequency of the cell. As one possibility the following equation may beused to estimate velocity based on doppler shift:

$v = {\frac{c}{f_{c}}*f_{d}}$

where f_(c) is the carrier frequency in hertz, f_(d) is the accumulatedDopper shift in hertz, and c is the velocity of light. In someinstances, such a doppler shift technique for estimating movement speedmay more particularly be used for certain types of cells, such as a cellin a high speed train network or a cell that is otherwise associatedwith high speed motion.

In addition or as an alternative to such motion estimation techniques, amovement speed or motion state of the wireless device may be determinedbased at least in part on how often/how many cell re-selections orhandovers have occurred recently and/or by what type of cells thewireless device has been recently served. As one such possibility, thewireless device may monitor how many cell re-selections or handovershave occurred within a certain (e.g., recent) time period (which may bereferred to as “T_(CRmax)”, e.g., in a 3GPP context), may determine inwhich range of multiple possible ranges (e.g., less than a parameter“N_(CR_M)”, between N_(CR_M) and a parameter “N_(CR_H)”, or greater thanN_(CR_H), as one possible set of ranges) the number of cellre-selections/handovers falls, and may determine a mobility state (e.g.,low, medium, or high, as one possible set of mobility states) of thewireless device corresponding to that range.

As another such possibility, the wireless device may monitor how manycells on which it has camped or otherwise detected within a certain(e.g., recent) time period are of a specific cell type, such as cellsassociated with high speed motion. For example, certain cells maybroadcast an indication that they are associated with high movementspeed (or an indication from which it may otherwise be inferred thatthey are associated with high movement speed), such as cells that areassociated with a high speed train network, and the wireless device maythus be able to determine whether its serving cell is such a highmovement speed cell, for each cell on which it camps/attaches (andpotentially also for some cells detected but not yet camped on). If thenumber of cells associated with high movement speed on which thewireless device has camped/attached (and/or more generally detected, ifdesired) within the specified time period is greater than a (e.g.,predetermined) threshold, the wireless device may determine that thewireless device has a high movement speed. Once such a determination ismade, the wireless device may consider itself to continue to have highmovement speed at least until a (e.g., predetermined) period of timepasses without a cell re-selection or handover to a new serving cellassociated with high movement speed (and possibly more generally withoutdetection of any new cells associated with high movement speed), atwhich time the wireless device may (e.g., possibly depending on othermovement speed indicators, such as any of those previously describedherein) no longer consider itself to have high movement speed.

Thus, based on any of a variety of possible conditions that may beindicative of movement speed of the wireless device, including any orall of those just described herein and/or any of various other possibleindicators, the wireless device may determine a movement speed and/ormobility state of the wireless device. The determined movementspeed/motion state may include a value (e.g., in any of various units ofspeed or velocity) and/or a relative state (e.g., low/medium/high/etc.)of motion encompassing a range of possible speed/velocity values, amongvarious possibilities.

In 504, the wireless device may perform cell searching and/or radio linkmonitoring based at least in part on the movement speed of the wirelessdevice. As previously noted herein, it may be beneficial to adjustcertain wireless device behaviors based on the movement speed of thewireless device, e.g., to provide features that are well suited to theparticular scenario in which the wireless device is currently operating.Two such areas of wireless device behavior that may be so adjusted basedon movement speed may include cell searches and radio link monitoring.

A wireless device may perform cell searching under any of a variety ofcircumstances. As one possibility, a wireless device may perform a cellsearch when it does not yet have service, e.g., to obtain an initialcell selection after being powered on upon toggling off airplane mode,or while out-of-service. As another possibility, a wireless device mayperiodically perform a cell search when in idle mode, e.g., to determinewhether to remain on the cell on which it is currently camped or toreselect to another (e.g., neighbor) cell. As yet another possibility, awireless device may perform a cell search after a radio link failureevent, e.g., to attempt to recover service (whether from its previousserving cell or another cell) after an interruption. Still anotherpossibility may include an X2L reselection, redirection, or blind fastreturn, e.g., from an older RAT after a circuit switched fallback (CSFB)or single radio voice call continuity (SRVCC) handover.

A cell search may commonly include scanning one or more frequencies onwhich cells may be deployed to determine whether any such cells arewithin communication range of the wireless device, potentially acquiringcell information for one or more candidate cells discovered in thefrequency scan, and further potentially attaching to a candidate cell ifa suitable such cell is found. The frequencies scanned during the cellsearch may include frequencies and/or frequency bands stored by thewireless device, e.g., in one or more databases.

As one possibility for adjusting a cell search procedure based onmovement speed of the wireless device, the order/priority in whichfrequencies are scanned may depend on the determined movement speed ofthe wireless device. For example, the wireless device may maintain a‘high speed’ database for frequencies associated with high speedmovement (e.g., cells that the wireless device has encountered that areassociated with a high speed train network) separate from one or moreother frequency databases (e.g., a more general acquisition database forfrequencies of cells that the wireless device has previouslyencountered) or may otherwise maintain information indicating that somesubset of its stored frequencies are associated with high movementspeed, and may more highly prioritize such frequencies when performing acell search while at a high movement speed than when performing a cellsearch while at a lower movement speed. Thus, for a cell search that isperformed while a wireless device has determined that it has a highmovement speed, one or more frequencies associated with high movementspeed may have a high priority may be earlier in the order in which thefrequencies are scanned), while for a cell search that is performedwhile a wireless device has determined that it has a lower movementspeed (e.g., does not have a high movement speed), one or morefrequencies associated with high movement speed may have a lowerpriority (e.g., may be later in the order in which the frequencies arescanned, or may not be scanned).

Radio link monitoring may include monitoring characteristics of a radiolink to help determine whether it is sufficient for the needs of awireless device. For example, radio link monitoring may includemonitoring a signal quality value (and/or other possible indicators oflink quality) for a radio link over a period of time to determinewhether the radio link is in-sync or out-of-sync over that period oftime. If the radio link is out-of-sync for too long without recovering,the radio link may be declared to have failed (e.g., a radio linkfailure (RLF) event may have occurred), which may trigger a RRCre-establishment procedure. If the RRC re-establishment procedure is notsuccessful, the wireless device may be forced into idle mode until a newRRC connection can be established (e.g., potentially with a new servingcell).

Since a wireless device moving at a high speed may move from cell tocell more quickly than a wireless device moving at a lower speed, it maybe possible that radio link monitoring parameters that provide goodperformance at lower speeds may result in poorer performance at higherspeeds. For example, if a serving cell is quickly weakening and thewireless device triggers RLF on a timeline selected for slower movementspeeds, a user may experience a longer service interruption beforereselection to a new cell with better signal quality is triggered thanif the wireless device were to trigger RLF on a timeline selected forfaster movement speeds. In contrast, radio link monitoring parametersselected for high movement speeds could result in premature RLFdeclaration (e.g., such that RLF is declared when a cell may stillrecover or when there may not be a more suitable cell yet) when awireless device is moving at lower movement speeds.

Thus, as one possibility for adjusting a radio link monitoring procedurebased on movement speed of the wireless device, one or more radio linkmonitoring parameters may be modified based at least in part on themovement speed of the wireless device, e.g., such that differentparameters may be used at high movement speeds than at lower movementspeeds. The parameters may include any of various parameters, includingbut not limited to an out-of-sync counter maximum (e.g., a number ofconsecutive and/or accumulated out-of-sync indications that triggersinitiation of an out-of-sync timer), a radio link monitoring windowlength (e.g., a period of time over which signal quality is monitored todetermine if an out-of-sync indication or an in-sync indication occurs),an out-of-sync timer length (e.g., a length of time after theout-of-sync counter maximum is reached that the radio link has torecover before radio link failure is declared), a signal qualitythreshold for determining if the wireless device is out-of-sync during aradio link monitoring window, and/or a signal quality threshold fordetermining if the wireless device is in-sync during a radio linkmonitoring window, among various possibilities.

In at least some instances, the radio link monitoring parametersselected may also depend on one or more other considerations, e.g., inaddition to movement speed of the wireless device. As one suchpossibility, the out-of-sync counter maximum (which may also be referredto as “N310”, e.g., in a 3GPP based implementation) and/or theout-of-sync timer length (which may also be referred to as “T310”, e.g.,in a 3GPP based implementation) may further depend at least in part on aconnected discontinuous reception (CDRX) cycle timer length currently inuse (e.g., since that may affect the radio link monitoring window). Forexample, a target amount of time for declaring RLF after initially goingout-of-sync (e.g., if no recovery occurs in the meantime) for a highspeed movement scenario may be determined, and the N310 and T310 valuesmay be adjusted such that RLF would occur after the target amount oftime in view of the current CDRX cycle timer length.

As another such possibility, the signal quality threshold fordetermining if the wireless device is out-of-sync during a radio linkmonitoring window (which may also be referred to as “Q_(out)”, e.g., ina 3GPP based implementation) may further depend at least in part on whatapplication or service type or types are currently active at thewireless device. For example, in some instances it may be the case thatVoLTE calls may suffer when at high movement speeds even at signalquality levels that may be sufficient at lower movement speeds, suchthat user experience may benefit (e.g., fewer calls may be dropped,voice quality may be improved, etc.) from use of a higher value forQ_(out) when VoLTE is active in a high movement speed scenario. Thus, inat least some instances, a higher signal quality threshold may be usedfor determining if the wireless device is out-of-sync when the wirelessdevice is at a high movement speed and when VoLTE (and/or one or moreother application or service types sensitive to signal quality at highmovement speeds) is active, than when the wireless device is at a lowermovement speed and/or when VoLTE (and/or one or more other applicationor service types sensitive to signal quality at high movement speeds) isnot active.

Additional Information

FIGS. 6-12 and the following information are provided as beingillustrative of further considerations and possible implementationdetails relating to the method of FIG. 5, and are not intended to belimiting to the disclosure as a whole. Numerous variations andalternatives to the details provided herein below are possible andshould be considered within the scope of the disclosure.

FIGS. 6-8—Movement Speed Determination

As described with respect to FIG. 5, it may be desirable in at leastsome instances to provide techniques for modifying cell searching, radiolink monitoring, and/or other behavior of a wireless device based onmovement speed of the wireless device, potentially including forscenarios when the wireless device is moving at relatively high movementspeeds, in order to apply such techniques, it may be important toprovide the capability to determine the movement speed of a wirelessdevice.

3GPP specification documents include criteria for determining a mobilitystate of a wireless device based on the frequency of cellreselection/handover. However, such techniques may not be able toaccurately identify very high movement speed (e.g., ˜300 km/h, as onepossibility) scenarios, such as might occur when moving in a high speedtrain. For example, 3GPP 36.304 section 5.2.4.3 describes a normalmobility state, a high mobility state, and a medium mobility state,along with parameters “T_(CRmax)”, “N_(CR_M)”, and “N_(CR_H)”, which maybe used to determine in which of those mobility states a wireless deviceis currently operating at a particular time. Those mobility states maytypically correspond to pedestrian movement (e.g., up to approximately 5km/h), movement by bike (e.g., up to approximately 30 km/h), or movementby car (e.g., up to approximately 120 km/h) ranges and may not allow fora higher range of movement speed (e.g., up to approximately 300 km/h)such as for movement by high speed train.

Since such existing techniques may be insufficient to identify when highspeed scenarios are occurring, it may be helpful to provide additionalor alternative indications of the movement speed of a wireless device.As one such possibility, it may be useful to attempt to calculate orestimate the velocity of the wireless device from one or moremeasurements that the wireless device may be capable of performing. Forexample, in some instances, a wireless device may be able to determineits velocity from one or more of a GPS unit, an LTE frequency offset,and/or motion sensing circuitry of the wireless device. A wirelessdevice may use a combination of such techniques, and/or may usedifferent techniques at different times, for example based on theavailability of those techniques and/or other considerations.

As another possibility for determining the movement speed of a wirelessdevice, it may be possible to infer the movement speed of a wirelessdevice based on the type of cells it has encountered, e.g., includingcells that it is camped on and/or has recently camped on. For example,it may be the case, at least in some instances, that cells for servingusers at such high movement speeds may be deployed for such scenarios;for example, a network of high speed train (“HST”) cells may be deployedalong a HST railway. Such cells may provide an indication (e.g., a“HighSpeedFlag” parameter provided in system information (e.g., a SIB2)broadcast by such a cell) that they are associated with high speedmovement (or more specifically with a high speed train network).According to some embodiments, such HST cells may have a typical cellcoverage of approximately 3 km, though any number of other cellcoverages are also possible. Thus, a wireless device may be able todetermine that a cell is associated with high movement speed when itencounters that cell, and may monitor the number of such HST cells thatit detects, on which it has camped, and/or to which it has attachedwithin a recent time period (“T_(hst_enter)”). If that number exceeds apredetermined threshold (“N_(hst_num)”), that may be considered anindication that the wireless device is moving at a high speed.

FIG. 6 is a graph illustrating a possible movement speed timeline for awireless device on a high speed train, according to some embodiments. Asshown, the wireless device may initially be stationary or moving at arelatively low speed (e.g., as the user enters the train), and mayaccelerate to reach an eventual steady movement speed. During such anacceleration phase 602, it may be possible to use velocity calculationsfrom GPS, and/or it may be possible to use acceleration measurementsfrom motion sensing circuitry (e.g., an accelerometer) of the wirelessdevice (e.g., if the GPS is disabled). At the steady speed phase 604, itmay also be possible to use velocity calculations from GPS, ifavailable. If GPS is not available (or it is otherwise desired), it maybe possible to estimate velocity from the doppler shift of cellular(e.g., LTE) signals communicated to the wireless device, and/or toestimate velocity based on the duration that the wireless device iscamping on an HST cell and/or based on whether N_(hst_num) is exceededin the most recent T_(hst_enter) window. After the steady speed phase604, the wireless device may slow down to lower speeds (e.g., as thetrain reaches a station and the user exits the train). In thisdeceleration phase 606, similar to the acceleration phase 602, it may bepossible to use velocity calculations from GPS, and/or it may bepossible to use acceleration measurements from motion sensing circuitryof the wireless device.

FIG. 7 is a flowchart diagram illustrating aspects of an exemplarypossible method for determining whether a wireless device is travellingat high speed, according to some embodiments. The method may be used inan LTE context (e.g., as shown) according to some embodiments, however,similar methods may also or alternatively be used for determiningwhether a wireless device is travelling at high speed when communicatingaccording to other RATs, as desired.

As shown, the wireless device may initially camp on an LTE cell (702).It may be determined whether the velocity as measured by a GPS module ofthe wireless device is above a predetermined velocity threshold(“V_(threshold)”) (704). If the velocity as measured by the GPS moduleis greater than V_(threshold), the it may be determined that thewireless device has a high movement speed (e.g., may be in a HST) (714).If the velocity as measured by the GPS module is less than V_(threshold)(or if the GPS measurements are not available), the wireless device maydetermine whether the velocity as measured by motion sensing circuitryof the wireless device is greater than V_(threshold)(706). If thevelocity as measured by the motion sensing circuitry is greater thanV_(threshold), the it may be determined that the wireless device has ahigh movement speed (714). If the velocity as measured by the motionsensing circuitry is less than V_(threshold) (or if measurements fromthe motion sensing circuitry are not available or inconclusive), thewireless device may further determine if the velocity as measured basedon doppler shift is greater than V_(threshold) (708), and if so, it maybe determined that the wireless device has a high movement speed (714).However, if the velocity as measured based on doppler shift is notgreater than V_(threshold), the wireless device may determine whetherthe number of camped (or possibly more generally detected) HST cellsduring T_(hst_enter)exceeds N_(hst_num) (710). If the number of campedHST cells during T_(hst_enter) does exceed N_(hst_num), it may bedetermined that the wireless device has a high movement speed (714).Otherwise, it may be determined that the wireless device does not have ahigh movement speed (712).

Note that the value of V_(threshold) may depend on one or morecharacteristics of a cell on which the wireless device is currentlycamped, according to some embodiments. For example, the value ofV_(threshold) could be different depending on whether the serving cellis a HST cell or a non-HST cell. Additionally or alternatively,different velocity threshold values may be used for any or all of thevelocity comparisons (e.g., in 704, 706, or 708), for example to accountfor potentially differing precision levels of the different velocityestimation techniques.

Thus, such a method may be useful as one possibility for accuratelyidentifying when a wireless device is moving at a high speed (e.g.,along a HST railway). In at least some instances, the basebandprocessor/domain of the wireless device may perform such a determinationand may provide an indication of whether it is moving at a high speed tothe application processor/domain of the wireless device. This may assistthe wireless device to more effectively implement any desired proceduresor techniques in a manner that depends on whether a wireless device ismoving at a high speed.

Alternatively or additionally, it may be possible to determine whether awireless device is in a high-speed train scenario in a manner morereliant on the cell history than on movement speed measurements. Aspreviously noted, a wireless device may be able to determine if a cellis a HST cell, at least in some instances, based on system informationbroadcast by the cell. A wireless device may maintain a HST databaseincluding frequencies of such cells, e.g., such that when a wirelessdevice switches to a new serving cell, its RRC layer may update thefrequency point into its HST database if <highSpeedFlag=true> isprovided in the SIB2 for the cell. Since HST cells may in at least someinstances be adjacent to non-HST cells (e.g., in the vicinity of a trainstation), it may be the case that users that live or otherwise areactive near a railway may have a non-empty HST database. Thus, in orderto avoid negatively impacting such users by mistakenly identifying themas being in a high-speed scenario, it may be important to carefullyconfigure any techniques for identifying whether a wireless device is ina high-speed train scenario based on the cell history of the wirelessdevice.

FIG. 8 is a state diagram illustrating possible states and statetransitions that could be used for monitoring whether a wireless deviceis in a high movement speed state based primarily on the cell history ofthe wireless device, according to some embodiments. As shown, there maybe a HST state 802 and a non-HST state 804 defined according to thestate diagram. The status of a wireless device may be judged on eachoccasion that a cell switch occurs and an SIB2 associated with the newcell is received, according to some embodiments. The entry conditioninto the HST mode may include the HST database timer of a frequencybeing reset/updated within a predetermined time period (“T_(entry)”),e.g., which may occur when a new HST serving cell is added to the HSTdatabase or a previously visited HST serving cell has its HST databasetimer reset as a result of being used as a serving cell again.

The exit condition from the HST mode may include the HST database notbeing updated for a predetermined time period (“T_(exit)”). Thus, thewireless device may not immediately leave the HST mode when goingout-of-service, when an HST cell deployment hole is encountered, whenexiting a train, or when temporarily stopping (e.g., at an intermediatestation), but may eventually leave the HST mode if such conditionspersist for sufficiently long. Additionally, this may help avoid usersliving along the railway line remaining indefinitely in the HST mode,e.g., as it may the case that such users may not perform handover orreselect new serving cells as rapidly as when travelling on a high speedtrain, and may thus exit the HST mode relatively quickly even if such amode is triggered due to proximity to a HST railway.

FIG. 9—High Speed Train Scenario

FIG. 9 is a diagram illustrating exemplary possible cell transitions fora wireless device moving on a high speed train, according to someembodiments. As previously noted, at least in some instances, high speedtrain cell networks may be deployed in the vicinity of high speed trainrailways. Such networks may deploy cells on different frequencies thanpublic networks, according to some embodiments. The HST Cells 902, 904,906, 908 illustrated in FIG. 9 may be representative of several cells ofa HST network, according to some embodiments.

In many locations, there may be one or more cells belonging to a publicnetwork in the vicinity of the cells of a HST network. The publicnetwork cells 912, 914, 916 illustrated in FIG. 9 may be representativeof several such cells, according to some embodiments. In some locations(e.g., railway stations), there may be mutual neighbor relationshipsbetween HST cells and public cells. In some locations (e.g., along arailway line), it may also be possible that there may be a one wayneighbor relationship from an HST cell to a public cell (e.g., LTE, GSM,UTRAN, etc.).

In such a case, after a wireless device moves to a public network (e.g.,due to CSFB, reselection, redirection, handover, out-of-service, or forany other possible reason), such as illustrated in cell transition 922of wireless device 910 from HST cell 902 to public network cell 912, thesubsequent cell transition(s) performed by the wireless device 910 maydepend considerably on the cell search technique(s) used by the wirelessdevice 910.

For example, while a wireless device may maintain a HST cell database(e.g., as previously noted), at least according to some embodiments, ifthe wireless device is not capable of accurately determining when it isin a HST scenario, it may still be possible for a wireless device tomistakenly prioritize HST cells when not in a HST scenario (e.g., ifadjacent to a high speed railway but not on a train), or to fail toprioritize HST cells when actually in a HST scenario (e.g., if awireless device moves to a public cell while on a train, such as in theillustrated cell transition 922 in FIG. 9).

In a situation in which a wireless device fails to recognize that it isin a HST scenario, it may not prioritize HST cells during cell searches(e.g., searching a standard acquisition database and/or performing aband scan when out-of-service (OoS) or performing an initial cellselection, or performing measurements on non-HST frequencies for X2Lre-selections/redirections), which may result in aselection/reselection/redirection to another public network cell, suchas illustrated in cell transition 924 of wireless device from publicnetwork cell 912 to public network cell 914. In such a situation, thewireless device 910 may continue such transitions (e.g., including celltransition 926 from public network cell 914 to public network cell 916)and may have difficulty returning to the HST network, potentiallyresulting in an increased rate of call drops, lost pagingindications/messages, and/or radio link failure occurrences.

In contrast, if a wireless device is able to recognize that it is in aHST scenario (e.g., even if it is not currently camped on a HST cell,such as by utilizing any of the movement speed/mobility statedetermination techniques described herein), it may be able to prioritizeHST cells during cell searches. For example, when OoS or performing aninitial cell selection or background X2L cell selection, a wirelessdevice may search HST frequencies prior to searching frequencies in thelegacy acquisition database and/or prior to performing a band scan.Similarly, for X2L reselection/redirection or blind fast return, the(e.g., LTE) HST database may be measured/searched with a higherpriority. This may include blind configuring the HST database formeasurements before the SIB (e.g., SI2quater) is received and adjustingHST frequency priority accordingly after the corresponding SIB isreceived for reselection, and/or configuring the HST database in the X2Lredirection list for redirection. This may result in a relatively rapidselection/reselection/redirection from OoS or from a public network(possibly non-LTE RAT) cell back to a HST network cell, such asillustrated in cell transition 928 of wireless device from publicnetwork cell 912 to HST network cell 904. In such a situation, thewireless device 910 may continue such transitions from HST cell to HSTcell, potentially resulting in decreased radio link failure rate, calldrop rate, paging loss rate, and/or overall improved usability and userexperience.

FIG. 10—Frequency Scan After Radio Link Failure Flowchart

In addition to cell searches such as those performed for initial cellselection, OoS cell searching, background X2L cell selection. X2Lre-selections/redirections, blind fast return and idle modere-selections, a wireless device may perform frequency scanning and cellsearching as part of a RRC re-establishment procedure after a radio linkfailure event until RRC re-establishment is successful or until a T311timer expires, according to some embodiments. At least in someinstances, the T311 timer may be set as a relatively short value (e.g, 1second long, as one possibility in a HST network cell), such that it maybe difficult to complete a full frequency scan and cell search prior toexpiration of the timer. After the T311 timer expires without successfulRRC re-establishment, the wireless device may enter idle mode, leadingto a potential service break and poor user experience. For example, ifthis occurs while a VoLTE call is active, a call drop may occur. Inorder to improve the likelihood of recovering service prior toexpiration of the T311 timer/reduce the likelihood of such serviceinterruptions, it may be useful to prioritize HST cells when performingfrequency scanning after a radio link failure event and prior toexpiration of the T311 timer when a wireless device is determined to beat a high movement speed or otherwise determined to be in a HSTscenario.

FIG. 10 is a flowchart diagram illustrating aspects of an exemplarypossible method for performing a cell scan after a radio link failureevent when a wireless device is moving at a high movement speed,according to some embodiments. As shown, the frequency scan may be splitinto multiple (e.g., 3) steps, which may help allow the wireless deviceto complete cell selection before the T311 timer expires. The wirelessdevice may first scan up to a predetermined number (“X”) of HSTfrequencies (e.g., from the HST database stored by the wireless device)(1002). It may be determined if this is successful (1004), and if so,the process may be complete. If not, the wireless device may next scanup to a predetermined number (“Y”) of normal frequencies (e.g., from alegacy acquisition database stored by the wireless device) (1006). Itmay be determined if this is successful (1008), and if so, the processmay be complete. If not, the wireless device may next scan up to anyremaining frequencies (e.g., from the HST database and/or the legacyacquisition database stored by the wireless device) (1010). Ifsuccessful, this may result in radio link recovery, or if unsuccessful,the T311 timer may expire, in either case resulting in completion of theprocess.

FIGS. 11-12—Movement Speed and/or Application Based Radio LinkMonitoring Flowchart

Radio link monitoring (RLM), e.g., as defined in 3GPP, may includetechniques for determining when cell coverage is too poor for use by awireless device. At least according to some embodiments, the radio linkmonitoring process may include determining radio link signal quality,and if it is below a certain threshold (Q_(out)), providing anindication from the lower layers to RRC that the radio link isout-of-sync. Upon receiving a certain number (N310) of consecutiveout-of-sync indications from lower layers, RRC may start a timer (T310).The T310 timer may be stopped or reset under certain conditions (e.g.,if the radio link recovers), however, if T310 expires, RRC may declareradio link failure.

In a high speed scenario (e.g., when traveling on a HST), it may bepossible that network configured RLM parameters (e.g., that may beintended for communication while at slower speeds) may not trigger RLFin a timely manner, which may result in poor downlink and/or uplink keyperformance indicators (KPIs) and/or potential mobile terminated callsbeing missed. For example, under a high speed scenario, SNR may degraderapidly (e.g., signal quality may drop below Q_(out) within is under aHST scenario, in some instances), but the out-of-sync indicationinterval may be the CDRX cycle length (e.g., if configured, or possiblyevery radio frame if CDRX is not configured), such that in a networkconfiguration with N310 equal to 20 and a CDRX cycle length of 320 ms,T310 may not be triggered until 6400 ms after signal quality falls belowQ_(out). This may result in a substantial service gap before thewireless device triggers RLF and attempts to recover service, e.g., on anew serving cell.

Additionally, some applications may be more sensitive to signal qualitywhen moving at high speeds. For example, in a high speed scenario, insome instances a VoLTE call may not work even when signal quality isabove Q_(out). Q_(out) may be defined in 3GPP as a signal quality levelresulting in a 10% block error rate for the PDCCH, which may be a worsesignal quality level than for PDSCH/PUSCH decoding. Thus, it may bepossible for a UL grant to be insufficient to support an uplink VoLTEpacket, e.g., if uplink transmission power is limited (e.g., may have amaximum power value “Pmax”), as the network may not assign sufficientuplink bandwidth and/or MCS may be low since uplink signal is poor. Forexample, consider a scenario in which a VoLTE call is established usingAMR codec rate of 23.85 kbps, such that 110 bytes may be required per 20ms. An uplink grant with (3 PRB, 0 MCS) may be limited to 7 bytes per 5ms, or 28 bytes per 20 ms, which may be insufficient for the voicepackets, resulting in most voice packets timing out and being discarded.When such a scenario occurs, the wireless device may be able to recoverthe VoLTE call if the wireless device performs handover or otherwisere-establishes to a new cell, but if cell signal quality is aboveQ_(out), the wireless device may remain in the serving cell.

Thus, if RLM parameters are not differentiated between high speed (e.g.,HST) and other scenarios, as may be common for at least some networks,wireless devices may suffer from the potentially long duration of theRLM process and/or from staying under a serving cell without triggeringRLF despite insufficient signal quality. Such problems may be remediedby taking some or all of movement speed, C-DRX cycle, and/orapplication/service type into consideration when performing RLM.Accordingly, FIGS. 11-12 are flowchart diagrams illustrating aspects ofexemplary possible methods for performing radio link monitoring based onmovement speed, C-DRX cycle, and/or application/service type, accordingto some embodiments.

As previously noted, the RLM parameters used when performing RLM mayinclude an N310 value, a T310 timer value, and/or a Q_(out) value. Onepossibility for performing RLM based at least in part on movement speedmay include modifying one or both of the N310 value and the T310 timervalue based on the movement speed and the C-DRX cycle length of awireless device. FIG. 11 is a flowchart illustrating such a method. Asshown, at each CDRX reconfiguration, it may be determined whether thewireless device is in a high speed scenario (1102). If the wirelessdevice is not in a high speed scenario, the network configured N310 andT310 values may be used. If the wireless device is in a high speedscenario, it may further be determined whether the total length of timefrom initially going out-of-sync to declaring radio link failure (i.e.,N310*DRX_cycle+T310) is greater than or equal to a desired length oftime (which may be referred to as “T_(fading)”) from initially goingout-of-sync to declaring radio link failure (1104). If it is not, thenetwork configured N310 and T310 values may be used. However, if it is,N310 and/or T310 may be set to modified (e.g., more aggressive) values(1106). For example, N310 may be adjusted based on the CDRX cyclelength, e.g., with values specified for each of various possible CDRXconfigurations (e.g., ‘N1’ for no CDRX, “N2” for CDRX_cycle=40 ms, “N3”for CDRX_cycle>=160 ms, as one possibility), while T310 may be limitedto a desired value “T_(recovery)”. The N1/N2/N3/T_(recovery) values maybe selected for good performance based on field testing, as onepossibility, or may be selected in any other desired manner. As onepossibility, the N1/N2/N3 values may be selected such that the length oftime from initially going out-of-sync to triggering the T310 timer maybe on the order of 100-200 ms, while T_(recovery) may be selected as1000 ms. As will be recognized, such values are provided forillustrative purposes only, and any other desired values mayalternatively or additionally be used, as desired.

Another possibility for performing RLM based at least in part onmovement speed may include modifying the Q_(out) value based on themovement speed and the service type(s) active at a wireless device. FIG.11 is a flowchart illustrating such a method, in particular in relationto voice call services in a high movement speed scenario. According tosome embodiments, the method of FIG. 12 may be performed when a wirelessdevice has already determined that it is in a high movement speedscenario. As shown, the wireless device may check the current voicepacket drop rate, e.g., including the drop rate of QCI=1 packets in theuplink buffer (1202). It may be determined if the drop rate is greaterthan a desired threshold (1204). If the drop rate is not greater thanthe desired threshold, the network configured Q_(out) value may be used(1206). However, if the drop rate is greater than the desired threshold,a modified (e.g., higher) Q_(out) value (“Q_(out_modified)”) may be used(1208). Note that the wireless device may repeat the methodoccasionally/periodically, such that if the drop rate falls below thedesired threshold again at a later time, the wireless device may resumeusing the network configured Q_(out) value. The Q_(out_modified) valuemay be selected for good performance based on field testing, as onepossibility, or may be selected in any other desired manner.

Such techniques may help prevent missed mobile terminated calls, mayhelp a wireless device re-establish to a potentially better cell morequickly, and/or may improve downlink and/or uplink KPIs, according tosome embodiments. Additionally, for VoLTE calls (and/or other servicesthat may be sensitive to signal quality at high movement speeds), use ofparameters leading to more aggressive RLF declaration and/or higherQ_(out) values may allow a wireless device to re-establish to a new andpotentially better cell (with potentially improved user experience) whennetwork configured parameters might lead to the wireless deviceremaining on a serving cell even when it is unable to support a VoLTEcall.

Embodiments of the present invention may be realized in any of variousforms. For example, in some embodiments, the present invention may berealized as a computer-implemented method, a computer-readable memorymedium, or a computer system. In other embodiments, the presentinvention may be realized using one or more custom-designed hardwaredevices such as ASICs. In other embodiments, the present invention maybe realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory medium(e.g., a non-transitory memory element) may be configured so that itstores program instructions and/or data, where the program instructions,if executed by a computer system, cause the computer system to perform amethod, e.g., any of a method embodiments described herein, or, anycombination of the method embodiments described herein, or, any subsetof any of the method embodiments described herein, or, any combinationof such subsets.

In some embodiments, a device (e.g., a UE) may be configured to includea processor (or a set of processors) and a memory medium (or memoryelement), where the memory medium stores program instructions, where theprocessor is configured to read and execute the program instructionsfrom the memory medium, where the program instructions are executable toimplement any of the various method embodiments described herein (or,any combination of the method embodiments described herein, or, anysubset of any of the method embodiments described herein, or, anycombination of such subsets). The device may be realized in any ofvarious forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

1-20. (canceled)
 21. An apparatus, comprising: at least one processorconfigured to cause a wireless device to: determine a mobility state ofthe wireless device; perform a cell search, wherein the cell searchcomprises scanning a plurality of cells within communication range ofthe wireless device; and select, as part of a reselection process, acell of the plurality of cells, wherein, when the mobility state of thewireless device corresponds to a high speed scenario, the reselectionprocess prioritizes selection of cells identified as high speed cells.22. The apparatus of claim 21, wherein the at least one processor isfurther configured to cause the wireless device to: receive a systeminformation block (SIB) from a first cell of the plurality of cells,wherein the SIB includes an indication the cell is a high speed cell;and identify the first cell as a high speed cell in the reselectionprocess based in the indication in the SIB.
 23. The apparatus of claim22, wherein determining the mobility state of the wireless devicecomprises determining the mobility state of the wireless devicecorresponds to a high speed scenario and wherein said selecting the cellof the plurality of cells includes selecting the first cell based on themobility state of the wireless device corresponding to the high speedscenario.
 24. The apparatus of claim 21, wherein, as part of thereselection process, when the mobility state of the wireless device doesnot correspond to a high speed scenario, the cells identified as highspeed cells have a lower priority.
 25. The apparatus of claim 21,wherein prioritizing selection of cells identified as high speed cellsincludes prioritization of one or more frequencies associated with highmovement speed.
 26. The apparatus of claim 21, wherein the at least oneprocessor is further configured to cause the wireless device to, at alater time: determine that the wireless device has not reselected to aserving cell associated with high movement speed for at least apredetermined period of time; and perform a second cell search, whereinthe high speed cells have lower priority during the second cell searchbased at least in part on determining that the wireless device has notreselected to a high speed cell for at least the predetermined period oftime.
 27. The apparatus of claim 21, wherein determining the mobilitystate of the wireless device is based on one or more of: an amount ofdoppler shift detected in cellular communication signals received by thewireless device; a velocity calculation based on information from aglobal positioning system (GPS) module of the wireless device; one ormore measurements performed by motion sensing circuitry of the wirelessdevice; or a number of cell re-selections and/or handovers that haveoccurred within a predetermined period of time.
 28. The apparatus ofclaim 1, wherein the at least one processor is further configured tocause the wireless device to: modify one or more radio link monitoringparameters for the wireless device based at least in part on determiningthe mobility state of the wireless device corresponds to a high speedscenario.
 29. A method, comprising: by a wireless device: determining amobility state of the wireless device; performing a cell search, whereinthe cell search comprises scanning a plurality of cells withincommunication range of the wireless device; and selecting, as part of areselection process, a cell of the plurality of cells, wherein, when themobility state of the wireless device corresponds to a high speedscenario, the reselection process prioritizes selection of cellsidentified as high speed cells.
 30. The method of claim 29, furthercomprising: receiving a system information block (SIB) from a first cellof the plurality of cells, wherein the SIB includes an indication thecell is a high speed cell; and identifying the first cell as a highspeed cell in the reselection process based in the indication in theSIB.
 31. The method of claim 30, wherein determining the mobility stateof the wireless device comprises determining the mobility state of thewireless device corresponds to a high speed scenario and wherein saidselecting the cell of the plurality of cells includes selecting thefirst cell based on the mobility state of the wireless devicecorresponding to the high speed scenario.
 32. The method of claim 29,wherein, as part of the reselection process, when the mobility state ofthe wireless device does not correspond to a high speed scenario, thecells identified as high speed cells have a lower priority.
 33. Themethod of claim 29, wherein prioritizing selection of cells identifiedas high speed cells includes prioritization of one or more frequenciesassociated with high movement speed.
 34. The method of claim 29, furthercomprising, at a later time: determining that the wireless device hasnot reselected to a serving cell associated with high movement speed forat least a predetermined period of time; and performing a second cellsearch, wherein the high speed cells have lower priority during thesecond cell search based at least in part on determining that thewireless device has not reselected to a high speed cell for at least thepredetermined period of time.
 35. A wireless device, comprising: anantenna; a radio operably coupled to the antenna; and at least oneprocessor operably coupled to the radio; wherein the antenna, radio, andat least one processor are configured to: determine a mobility state ofthe wireless device; perform a cell search, wherein the cell searchcomprises scanning a plurality of cells within communication range ofthe wireless device; and select, as part of a reselection process, acell of the plurality of cells, wherein, when the mobility state of thewireless device corresponds to a high speed scenario, the reselectionprocess prioritizes selection of cells identified as high speed cells.36. The wireless device of claim 35, wherein the at least one processoris further configured to cause the wireless device to: receive a systeminformation block (SIB) from a first cell of the plurality of cells,wherein the SIB includes an indication the cell is a high speed cell;and identify the first cell as a high speed cell in the reselectionprocess based in the indication in the SIB.
 37. The wireless device ofclaim 36, wherein determining the mobility state of the wireless devicecomprises determining the mobility state of the wireless devicecorresponds to a high speed scenario and wherein said selecting the cellof the plurality of cells includes selecting the first cell based on themobility state of the wireless device corresponding to the high speedscenario.
 38. The wireless device of claim 35, wherein, as part of thereselection process, when the mobility state of the wireless device doesnot correspond to a high speed scenario, the cells identified as highspeed cells have a lower priority.
 39. The wireless device of claim 35,wherein prioritizing selection of cells identified as high speed cellsincludes prioritization of one or more frequencies associated with highmovement speed.
 40. The wireless device of claim 35, wherein the atleast one processor is further configured to cause the wireless deviceto, at a later time: determine that the wireless device has notreselected to a serving cell associated with high movement speed for atleast a predetermined period of time; and perform a second cell search,wherein the high speed cells have lower priority during the second cellsearch based at least in part on determining that the wireless devicehas not reselected to a high speed cell for at least the predeterminedperiod of time.